linux-kernel - Re: [PATCH 4/8] vmscan: Do not writeback filesystem pages in direct reclaim

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Message-ID: <20100719142621.GP13117@csn.ul.ie>
Date:	Mon, 19 Jul 2010 15:26:22 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 4/8] vmscan: Do not writeback filesystem pages in
	direct reclaim

On Mon, Jul 19, 2010 at 10:19:34AM -0400, Christoph Hellwig wrote:
> On Mon, Jul 19, 2010 at 02:11:26PM +0100, Mel Gorman wrote:
> > As the call-chain for writing anonymous pages is not expected to be deep
> > and they are not cleaned by flusher threads, anonymous pages are still
> > written back in direct reclaim.
> 
> While it is not quite as deep as it skips the filesystem allocator and
> extent mapping code it can still be quite deep for swap given that it
> still has to traverse the whole I/O stack.  Probably not worth worrying
> about now, but we need to keep an eye on it.
> 

Agreed that we need to keep an eye on it. If this ever becomes a
problem, we're going to need to consider a flusher for anonymous pages.
If you look at the figures, we are still doing a lot of writeback of
anonymous pages. Granted, the layout of swap sucks anyway but it's
something to keep at the back of the mind.

> The patch looks fine to me anyway.
> 

Thanks.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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